Radio frequency (RF) equipment uses a variety of approaches and structures for receiving and transmitting radio waves in selected frequency bands. Typically, filtering structures are used to maintain proper communication and frequency bands assigned to a particular band. The type of filtering structure used often depends upon the intended use and specifications for the radio equipment. For example, dielectric and coaxial cavity resonator filters are often used for filtering electromagnetic energy in certain frequency bands, such as those used for cellular and PCS communications.
The "ripple" of a radio wave filter arrangement is defined as the fluctuation of the frequency response in the passband of the filter of the filter arrangement. Various coded division multi-access (CDMA) cellular telephone applications require the ripple of a filter arrangement to be less than a predetermined level, such as 0.5 dB within a continuous passband of 1.23 MHz or 2 MHz.
A prior approach for reducing the ripple of a filter arrangement uses a filter having a relatively large Q factor. However, this approach requires a large resonator cavity for the filter, along with a sophisticated design and production process. Therefore, while other designs may effectively reduce the ripple of a filter arrangement, they do so with accompanying additional expenses resulting from added design and production costs. A filter arrangement that addresses the above-identified problems would therefore be desirable.